[llvm] r313245 - [SelectionDAG] ComputeNumSignBits - cleanup ROTL/ROTR wrapping to match DAGCombine etc.

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Thu Sep 14 03:28:01 2017
New Revision: 313245

URL: http://llvm.org/viewvc/llvm-project?rev=313245&view=rev
Log:
[SelectionDAG] ComputeNumSignBits - cleanup ROTL/ROTR wrapping to match DAGCombine etc.

Use RotAmt.urem(VTBits) instead of AND(RotAmt, VTBits - 1)

TBH I don't expect non-power-of-2 types to be created, but it makes the logic clearer and matches what we do in other rotation combines.

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp?rev=313245&r1=313244&r2=313245&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp Thu Sep 14 03:28:01 2017
@@ -3124,16 +3124,16 @@ unsigned SelectionDAG::ComputeNumSignBit
   case ISD::ROTL:
   case ISD::ROTR:
     if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
-      unsigned RotAmt = C->getZExtValue() & (VTBits-1);
+      unsigned RotAmt = C->getAPIntValue().urem(VTBits);
 
       // Handle rotate right by N like a rotate left by 32-N.
       if (Op.getOpcode() == ISD::ROTR)
-        RotAmt = (VTBits-RotAmt) & (VTBits-1);
+        RotAmt = (VTBits - RotAmt) % VTBits;
 
       // If we aren't rotating out all of the known-in sign bits, return the
       // number that are left.  This handles rotl(sext(x), 1) for example.
       Tmp = ComputeNumSignBits(Op.getOperand(0), Depth+1);
-      if (Tmp > RotAmt+1) return Tmp-RotAmt;
+      if (Tmp > (RotAmt + 1)) return (Tmp - RotAmt);
     }
     break;
   case ISD::ADD: